The invention relates to a processing apparatus, especially a granulating or coating apparatus, comprising a filtering assembly arranged above or adjacent to a processing chamber for removing dust from process air containing particulate material. The filtering assembly comprises at least one filter through which the process air flows from the processing chamber.
A processing apparatus of the mentioned type is known from the German patent DE 40 30 086. In such processing apparatus the process air flowing in the apparatus is used as a carrier medium for uniform distribution or for fluidizing the particulate material in the processing chamber. When passing through the filtering assembly for removing dust it is necessary to separate the particulate material from the process air so that the process air after filtering departs from the apparatus free of dust. The filter however not only has the purpose of removing dust, but also serves to retain particulate material in the processing chamber and optionally return it to the process itself.
A special application relates to a granulating apparatus. Small particles nearly the size of dust are agglomerated into larger particles in the processing chamber. The fluidized particle-like material is treated with a fine spray of liquid, which promotes agglomeration of the individual particles.
Another special application is the so-called coating process. A surface coating is formed on the particulate material suspended in the processing chamber in the process air by means of a liquid spray.
The process air in such apparatus is guided from the processing chamber in the lower region of the apparatus upwardly or sidewardly through the filtering assembly, for example by generating a corresponding vacuum in an exhaust chamber located above or adjacent to the processing chamber. The particulate material is retained by the filtering assembly and therefore cannot escape the processing chamber.
Depending on the properties of the particulate material, which can be present in the form of powder, pellets or granules, a portion of the material adheres to the filter or filters of the filtering assembly. Generally, the tendency to adhere is larger for finer, wetted or sticky particles than it is for larger or dry particles.
Due to the more or less pronounced tendency of the material to adhere to the filter or filters of the filtering assembly, it is necessary to free the filter or filters during the go process from deposited particulate material to avoid the filter from becoming impermeable to the process air and the process air flow being strongly reduced or even blocked. In addition, the deposited material removed from the filter or filters should be returned to the process. After completing a process and before beginning a new process, the filter or filters must be disassembled from the apparatus for complete cleaning for example with a washing fluid. A thorough cleaning is necessary, especially when a different particulate material is used in the subsequent process.
The apparatus disclosed in DE 40 30 086 comprises a filtering assembly having several filter cartridges arranged in a circle at the same elevation. Each filter cartridge consists of a vertically extended filter basket composed of a metal frame. A fabric filter sack is drawn over the basket as the filter medium, which forms the filter surface of the filter cartridge. The filter basket comprises a cylindrical outer portion and a cone-shaped inner portion.
A disadvantage of this filter cartridge is its considerable construction height. Because of this, the air space available for the processing chamber located below the filtering assembly is small for the given height of the apparatus. The active surface of each filter extends deeply into the processing chamber due to the filter construction, where the load on the filtering surface of each cartridge is particularly high. The filtering surface in the lower region of the filter cartridge is very strongly subjected to particulate material contained in the process air.
However, the considerable height of the known filter is necessary to achieve a sufficiently large active filtering surface, which makes a high through-put possible and maintains a sufficiently strong air flow for the process.
An air filter arrangement for an aspiration device is disclosed in the German patent application DE 35 15 641, which comprises a radially folded filter element with a number of folds. The German utility model DE 84 27 328 discloses an air filter for a vacuum cleaner, where the air filter has a bonnet-like or a bell-like shape. The filter includes a folded filter surface.
A plate filter is disclosed in the German patent application DE 41 47 550 formed of a web material folded in zig-zag shape, whose individual fold lines or filter surfaces run in a direction parallel to one another. This known plate filter is used for filtering the interior space of a motor vehicle.
An object of the present invention is to provide an improved processing apparatus of the above-mentioned type having a relatively enlarged processing chamber but without enlarging the processing apparatus on the whole.
According to the present invention the afore-mentioned object is achieved by a processing apparatus, comprising:
a processing chamber;
a filtering assembly arranged adjacent said processing chamber for removing dust from process air containing particulate material, said filtering assembly including at least one filter being passed by said process air coming from said processing chamber,
wherein said filter comprises a plurality of filter surfaces arranged adjacently to form a substantially circular filter body, said filter surfaces extending substantially radially and being inclined in meander-like geometry with respect to the flow of said process air, and wherein said filter body and said filter surfaces are made of a metallic multi-layer fabric.
In the processing apparatus according to the present invention, the total active filter surface of the filter can be substantially increased over the known filter cartridge due to the plurality of filter surfaces arranged adjacently in a meandering structure, so that the construction height of the filter and therefore that of the filtering assembly in the processing apparatus can be substantially reduced, while achieving a comparable filtering effect. Due to the plurality of filter surfaces, interconnected in meander-like manner, the total filtering surface can be concentrated into a disk shape space of reduced height. The space available for the process air in the processing chamber is therefore effectively enlarged without constructively enlarging the processing apparatus. In addition, due to the enlarged filtering surface obtained by the meandering of the filter surfaces forming the filter body, a single filter is sufficient to achieve a sufficient filtering of the process air. In contrast, a plurality of filter cartridges are provided to achieve a sufficient filter effect in the prior art. This provides a further advantage in that a substantial reduction in cost is achieved with the processing apparatus of the present invention.
The filter is fabricated from a metallic multi-layer fabric. A metallic multi-layer fabric has the advantage that it is inert and has high chemical resistance. Compared to textile filter media, it also has the advantage of high mechanical stability.
The radially extending filter surfaces, being inclined in meander-like geometry with respect to a vertical line, form in respective pairs steep roof-shaped caverns, open to the bottom, for example substantially v-shaped caverns. It will be understood that xe2x80x9cinclined with respect to the process air flowxe2x80x9d means that the filter surfaces in mounted condition of the filter are sloped with respect to the main direction of process air flow.
In a preferred embodiment, the filter is arranged substantially horizontally above the processing chamber.
A further advantage here is that the filter surfaces are located at a larger distance from the floor of the processing chamber in a processing apparatus of the same construction height as in the known apparatus. Consequently, the load on the filter is smaller than the filter cartridges of the known apparatus, because the concentration of particulate material in the process air decreases with increased distance from the floor of the processing chamber. The height of the apparatus of the present invention can even be reduced compared to the conventional apparatus. The vertical flow of the process air can be passed to the filter uniformly and nearly free of turbulence, which increases the fall velocity of the particulate material and considerably reduces the load on the filter itself.
In a preferred embodiment, a ratio of the height to the radial extension of the filter surfaces is less than 1.
This ratio is substantially greater than 1 in the filter cartridges of the known apparatus, while in the present invention, the construction height of the filter and also the filter load can be considerably reduced as mentioned. A further advantage is that the process air space in which the particulate material is handled is enlarged and therefore the result of granulating and coating processes are qualitatively and quantitatively improved.
Preferably, the ratio is in the range of about 0.1 to 0.5.
This has the advantage that a very flat filter is provided, which still fulfills the requirement on filtering effect to a sufficient degree.
In a further preferred embodiment, the filter body and the filter surfaces are made of the same material.
This is in contrast to the filter cartridges of the known apparatus having a metallic filter basket and a textile filter sack. The advantage of the present filter is that it is composed of the same medium, i.e. the filter body and the filter medium are made of the same material, which reduces the manufacturing cost of the present filter and in addition simplifies its manufacture. The present filter has a high static stability due to the meander-like geometry, so that a support structure such as the metal basket of the known filter cartridge is not needed.
The present filter can be produced in a simple and inexpensive manner, for example by folding one or more flat circular blanks of the metallic multi-layer fabric along radial folding lines to form a meandering structure. When the filter is formed of several starting blanks, these are welded or glued to one another after folding to form the circular filter body.
In a further preferred embodiment, each individual filter surface tapers in radial direction from the outside to the inside in ray-like manner.
This feature has the advantage that the slope or opening angle between two neighboring filter surfaces remains constant over the entire radial length of the filter surfaces. The advantage is that no twisting or deformation occurs in the filter material which could impair the filter effect. A major portion of the process air in the granulating and coating apparatus flows upwardly in the peripheral region of the processing chamber. Thus the reduced active filter surface toward the center of the filter having approximately trapezoidal-shaped filter surfaces, does not produce a noticeable impairment of the filter effect. In contrast, a reduced slope or opening angle between the filter surfaces toward the center of the filter would have the disadvantage that more particulate matter would be deposited between the more closely adjacent filter surfaces toward the center. Such deposits would be difficult to clean from the narrow gaps between the filter surfaces and precisely this is avoided.
In a further preferred embodiment, the intermediate spaces between neighboring filter surfaces are radially open at the outer periphery of the filter.
The feature has the advantage that the filter body apart from the meandering filter surfaces has no further surfaces, which would hinder a thorough cleaning of the filter after a process, so that the cleaning properties of the filter are further improved. The filter can easily be cleaned with a washing fluid after completing a process, where the washing fluid can flow outwardly from the cavern-like intermediate spaces formed between the filter surfaces.
In a further preferred embodiment, at least one ring is connected at the outer circumference with the end edges of the filter surfaces, where the width of the ring is smaller than the height of the end edges of the filter surfaces.
The at least one ring has the advantage of providing further form stability to the filter, where the small width of the ring allows the intermediate spaces between the filter surfaces to be substantially radially open at the end edges. The at least one ring can be formed for example of a thin ring band. Preferably, two radially spaced rings are provided for stabilizing the filter which are adhered or welded to the end edges.
In a further preferred embodiment, the filter surfaces are formed to have a concave curvature in the flow direction of the process air.
This feature has the advantage that the intermediate spaces between the filter surfaces on the side facing the processing chamber, i.e. the filter-active side of the filter has a larger filtration space. The upward velocity of the process air containing the particulate material is reduced due to the larger cross-section of the intermediate spaces between the filter surfaces, whereby the load on the filter is advantageously reduced.
In a further preferred embodiment, the filter comprises a central closeable opening.
Since the process air as mentioned flows upwardly substantially in the peripheral region of the processing apparatus, the center of the filter is only slightly passed by the process air and is therefore inactive as a filter. The opening at the center of the filter however allows the possibility of positioning a pneumatic or electric agitator, which shakes the filter during the process to shake off the particles adhering to the filter surfaces. If such an agitator is not employed, the opening can be tightly closed by a cover adapted to the opening.
In addition, the opening at the filter center simplifies the production of the meandering geometry of the filter surfaces by folding a metallic multi-layer fabric. The diameter of the opening can be 10 to 30% of the total diameter of the filter. Preferably the filtering assembly comprises one filter whose diameter corresponds approximately to the diameter of the processing chamber.
This feature has the advantage that the assembly of the filtering assembly in the processing apparatus as well as disassembly is substantially simplified, while the processing apparatus known from the prior art comprises a filtering assembly with a total of 4 to 10 filter cartridges, which require a corresponding increase in assembly work. Furthermore, the costs of the processing apparatus according to the present invention are reduced, because the complicated and costly support plates for several conventional filter cartridges in the known processing apparatus can be relinquished.
In a further preferred embodiment, where the filter comprises a central opening, a driving means for agitating the filter is arranged in the opening of the filter.
This feature has the advantage that a constructively simple possibility is provided for cleaning the filter, especially one which operates continuously. In addition to the lesser tendency of the particles adhering to the filter, the means for agitating the filter reduce the adherence further, because the agitated filter throws off a portion of the particles back into the processing chamber. A sufficient cleaning and return of larger and substantially non-adhesive particles is achieved to a satisfactory extent during the process. The drive of the agitating means is preferably electric or pneumatic.
In a further preferred embodiment, the filtering assembly comprises a circumferential first seal for sealing an outer circumference of the filter against an inner wall of the processing chamber, where the seal is removable from the filter.
This feature has the advantage that the seal can be removed from the filter after completing the process, where the filter can be assembled and disassembled and cleaned in a simpler and faster manner.
In a further preferred embodiment, when the filter has a central opening, the filtering assembly comprises a circumferential second seal for sealing an inner circumference of the at least one filter, where the seal is removable from the filter.
This feature also has the advantage that the filter body can be completely opened after completing a process, where the cleaning properties of the filter are further improved.
In a further preferred embodiment, the first seal and/or second seal are radially elastically expandable and comprise a hollow space which can be supplied with compressed air.
This feature has the advantage that on the one hand a highly effective seal is achieved between the filter and the inner wall of the processing apparatus due to the pneumatic force of the seal, because the seal is pressed against the inner wall and against the filter with high pressure. On the other hand, the pneumatic seal allows a rapid and simple assembly and disassembly of the filter in the processing apparatus. By applying compressed air to the hollow space in the seal, the first or second seal expands elastically in radial direction and presses against the outer circumference or the inner circumference of the filter on the one hand and against the inner wall of the processing apparatus or the cover at the center of the filter on the other hand. The pressure in the hollow space of the first or second seal is released to remove the filter, where the seal contracts elastically and can be removed from the filter.
In a further preferred embodiment, the first seal and/or the second seal comprise a circumferential separation joint, which allows a vertical shifting of the filter when exceeding a threshold value of a force acting in the vertical direction.
The feature has the advantage that if a blow-out occurs in the processing chamber, energy can be removed from the resulting pressure wave by vertical displacement of the filter, where it is then prevented that the processing apparatus would burst and a danger would arise to the operating personnel.
In a further preferred embodiment of the processing apparatus, the filtering assembly comprises radially displaceable securement elements for securing the filter in the processing apparatus.
The ease of operation of the present processing apparatus when mounting and dismounting the filter is further improved. For example, three to six such securement elements can be provided on the inner wall of the processing apparatus and are distributed about its circumference. The securement elements are preferably moveable in radial direction via pneumatic control, where the securement elements are preferably formed as carrier elements.
In a further preferred embodiment, means are provided above the filter for clearing the particulate material from the filter during a process.
This feature is of particular advantage when the process air includes very fine, especially sticky or moist particles, which have a high tendency to adhere to the filter. The means for clearing particulate material during the process enable an improved recovery of the material in the processing chamber.
Preferably, the clearing means comprise at least one rotatable arm which can be supplied with compressed air, whose length corresponds approximately to the radial extension of the filter surfaces and whose underside comprises at least one air outlet nozzle.
This feature has the advantage that a continuous cleaning of the filter is achieved during the running process, without the process airflow upwardly through the filter having to be interrupted for a cleaning. In the known processing apparatus in contrast, some of the filter cartridges are blocked off from the process air flow at regular intervals for cleaning the filter sacks and are subjected to the flow of a cleaning gas in opposite direction. The present arm is preferably configured to extend over a pair of filter surfaces of the filter, so that a large portion of the filter surfaces always remains subject to the passage of process air.
In a further alternative embodiment, the clearing means comprise a rotatable arm having a profile such that a downwardly directed pressure wave is generated by rotation of the arm.
This feature has the considerable advantage that no additional air flow is required, for example a cleansing gas, for removing particles from the filter. Moreover, a pressure wave is generated by rotation of the arm between the at least one arm, preferably provided in the form of an inclined rotor blade, which continuously reverses the process air stream passing through the filter. Since the supply of external cleansing air is not required, contamination of the particulate material being treated in the processing chamber is advantageously avoided. Furthermore, the costs of the processing apparatus according to the present invention are further reduced, because the cost-intensive treatment equipment for the supply of cleansing air can be relinquished.
In a further preferred embodiment, means for washing the filter are provided above the filter including a washing fluid.
This feature has the advantage that the filter does not need to be disassembled for washing between two processes, especially those involving the same particulate material, but can be washed in situ in the apparatus. It is sufficient that the above-mentioned seals be removed before washing the filter to also be able to clean the outer end edges of the filter surfaces. The washing means can also be used to bind the dustlike particles to the filter before disassembling, so that the material does not fall off and the operating personnel does not come into contact with the material.
The washing means preferably comprise a rotatable spray arm having at least one outlet for washing fluid on its underside.
This feature has the advantage that the washing means are constructively simple and inexpensive to manufacture. The outlet can be configured such that the filter can be selectively cleaned with a fluid jet, a fluid spray or with a surge of fluid.
In a further preferred embodiment, the washing means are integrated with the clearing means.
This feature has the advantage that the space requirement for the clearing means and the washing means is small, where only a small obstruction to process air flow is present above the filter. A further advantage is that the at least one spray arm of the washing means can be used for the inner cleaning of the clearing means. A further advantage is that only one drive mechanism is needed for both means.
Further advantages result from the following description and the attached drawings. It will be understood that the abovementioned features and those to be discussed below are applicable not only in the given combinations, but may also be used in other combinations or taken alone without departing from the scope of the present invention.
Embodiments of the inventions are illustrated in the drawings and will be discussed in more detail in the following.